Wolfram Alpha http://www.wolframalpha.com/
I use this as a teaching aid for solving all kinds of math problems and any chemistry element, formula, or equation. Also saw a Youtube of a 4th grade teacher/students using.
Laurie Rasmussen
math, science, college, all

Class marker: http://www.classmarker.com/
This is on line testing. I use this for checking homework.
Laurie Rasmussen
all, math, science, test, quiz

Khan Academy __http://www.khanacademy.org__/
Math and Science lesson plans with video. I use as tutorials, when absent, or for whenever.
Laurie Rasmussen
math, science, college

Educational Blogs by discipline http://movingforward.wikispaces.com/Education+Blogs+by+Discipline
Laurie Rasmussen
all

Kubbu http://www.kubbu.com/
I use this site for testing, you can add different kinds of questions and also practice activities.
Juliana Smith
test, quiz, homework

Lingro http://lingro.com/
This is a dictionary for several different languages and it says if it is a noun, verb, adjective, etc. It works better than the translators out there.
Juliana Smith
dictionary, translator

Voicethread http://voicethread.com/#home
This is a collaboration tool where students can make oral, video or written comments about pictures or videos. Since it is online anyone can access it and comment on it too. Also, can be shared by more than one person to make editing possible.
Juliana Smith
collaboration, recording, voice, pictures, videos

High School ACE http://highschoolace.com
This is a site with different activities in different subject matters to use for practice or reinforcement.
Juliana Smith
help, homework, activities

Make your own motivational posters - http://diy.despair.com/motivator.php - http://bighugelabs.com/motivator.php - http://wigflip.com/automotivator/
Tim Limbert
motivation, all

Lingtlanguage - http://lingtlanguage.com/home/
I use this site for oral tests and for quick activities. You can add text, picture, video or voice. Students can respond using voice or text.
Juliana Smith
homework, test, oral, activity, recording

Two questions that you can ask yourself everyday. http://vimeo.com/8480171
This is not only a reflective tool for yourself, but could be used for academic and athletic motivation.
Jeff Dicks
All, elementary, middle, high

Timerime http://timerime.com/
This is a site you can create timelines and you can have others edit your timeline by sharing it with them.
Juliana Smith
all, timelines, history, geography, language

122 for You: Cool Cat Teacher's favorite apps, software and sites http://coolcatteacher.blogspot.com/2009/04/122-for-you-cool-cat-teachers-favorite.htmlFound this from one I follow on Twitter. Provides resources for authoring, blogging, networking, bookmarking, video, production,calendaring, and also includes "trusty classroom standbys."
Randy Nielsen
All, Elementary, Middle, High

Manipula Math - http://ow.ly/1eDOb
Collection of hundreds of JAVA math applets for middle school, high school, and college.
Tim Limbert
math, middle, high, college

Best websites to download eBooks - http://ow.ly/1eDzITim Limbert
ebooks, high, middle

Aviary - http://aviary.com/blog/posts/free-online-editing#13Online multimedia editing tools, now free.
Tim Limbert
high, middle, graphics, photo

Flixtime - http://www.flixtime.com/Free online video slideshow creator
Tim Limbert
video, high, middle, elementary

Web sites with free resources for PBL (Project Based Learning)
http://www.pblassociates.com/websites_about_PBL.htm
http://www.thommarkham.com
"The Take Action Project" at www.takeactioncurriculum.org
NSTA's latest Science Scope: Community Based Learning
http://www.nsta.org/publications/browse_journals.aspx?action=issue&id=10.2505/3/ss10_033_07
http://www.clrn.org/weblinks/
Mary Kohnen
Lessons, Activities

slideshow with audio and captions: http://animoto.com/ http://photopeach.com/ http://www.fotobabble.com/
these are great for short slideshows and fotobabble is great for taking a picture and adding your own audio.
Laurie Rasmussen
elementary, middle, high

Jeopardy http://jeopardylabs.com/|
templates are already made and some games are already done
Laurie Rasmussen
elementary, middle, high

Onverse - http://www.onverse.com/invite.aspx?r=87877
A new virtual world, similar to Second Life, but simpler and with a lower age limit (13+).
I'm currently looking into educational/professional uses for this, and am talking with the developers.
This does take an application installed on the computer, it's not totally web-based.
Tim Limbert
High, Middle

To make collages of pictures use http://www.photovisi.com/
Laurie Rasmussen
elementary, middle, high

Resources for teens to find a real-world audience - http://ow.ly/1oJxn
Great place to submit writing for an English class (had an English teacher who regularly submitted writing to Teen Ink - kids loved it!)
Also, looks like some interesting ideas for math and science
middle, high
Alynn Coppock

Making a landscape design or floor plan http://v3.planningwiz.com/
all, elementary, middle, high
Laurie Rasmussen

Partnership for 21st Century Skills http://www.p21.org/
Great framework by content area for implementing 21st Century Skills
Jeff Dicks

Class Chatter - An interesting site to begin blogging with your students.
Alynn Coppock

Bib 2.0 http://bib20.blogspot.com/2010/06/supplement-your-streaming-video-with.html
Marlise Witham
Free documentary resources. Over 1200 videos (similar to Discovery Streaming). This site offers a wide variety of topics, ranging from history to science to psychology and literature, many from Nova, the History Channel, etc. The database is searchable by topic or key word. The site presents each video on a blog-like page, with a brief text introduction, followed by the embedded video.